Not surprised you got mixed reviews. It's a much more complicated question than it seems.
There are two main things: show and non showing- pet, utility etc. A majority it seems are interested in pet or utility and color is not important . For that "market", it is perfectly allright to mix the colors. With show stock, it really really is best to have the colors separated at breeding because while solid black, solid buff, solid white seem to be such "simple" colors but solid buff is one of the most genetically 'complicated'(many genes) and so the hardest to maintain and the quickest to 'mess up'- will be a long time to get solid buffs again if mixed with another color.
Black is a little simpler but it does require being pure for a couple genes for them to stay solid black and the tricky part is they have the problem of chicks growing up seemingly solid black only to get some off-color once they mature and some hens not pure for "solid black" can be visually solid black but keep throwing her not-pure genes to chicks and off color can show up in these.. making a solid black line a 'long term project' if mixed up.
Example: breeding solid black to a red or buff will give chicks that seem solid black but they will show off color as they mature(pictures of black sex links are great examples of this), and so they can't be shown or sold to people interested in showing.
However there are some exceptions- white. White is not a color, it's merely a gene that prevents pigmentation from being put into the feather. They can be genetically any color under the sun but you can't see it. Most whites are genetically black chicken because this combination tends to produce a cleaner, crisper white. Genetic black chickens can be mixed with black chickens 'just fine' for this reason.. except IIRC, the show standard calls for clean yellow legs in whites and black legs on blacks.. which is a problem because for whites with yellow legs the trick is to breed in barred, sex linked dilution, possibly with other things like mottle as these also have an effect on skin pigmentation and they turn otherwise black legs into clean yellow legs. If barred/cuckoo NN is your interest, you could mix them with whites for this reason.. they'd all be supposed to have as yellow legs as possible anyways...
Buff to red is not a good idea either, as buff is very complicated and hard to get even buff coloring.. getting buff roosters without darker shade saddles than body would be a big problem if they were crossed.
as you see- so much detail and differences, not an easy one to answer.
There are two main things: show and non showing- pet, utility etc. A majority it seems are interested in pet or utility and color is not important . For that "market", it is perfectly allright to mix the colors. With show stock, it really really is best to have the colors separated at breeding because while solid black, solid buff, solid white seem to be such "simple" colors but solid buff is one of the most genetically 'complicated'(many genes) and so the hardest to maintain and the quickest to 'mess up'- will be a long time to get solid buffs again if mixed with another color.
Black is a little simpler but it does require being pure for a couple genes for them to stay solid black and the tricky part is they have the problem of chicks growing up seemingly solid black only to get some off-color once they mature and some hens not pure for "solid black" can be visually solid black but keep throwing her not-pure genes to chicks and off color can show up in these.. making a solid black line a 'long term project' if mixed up.
Example: breeding solid black to a red or buff will give chicks that seem solid black but they will show off color as they mature(pictures of black sex links are great examples of this), and so they can't be shown or sold to people interested in showing.
However there are some exceptions- white. White is not a color, it's merely a gene that prevents pigmentation from being put into the feather. They can be genetically any color under the sun but you can't see it. Most whites are genetically black chicken because this combination tends to produce a cleaner, crisper white. Genetic black chickens can be mixed with black chickens 'just fine' for this reason.. except IIRC, the show standard calls for clean yellow legs in whites and black legs on blacks.. which is a problem because for whites with yellow legs the trick is to breed in barred, sex linked dilution, possibly with other things like mottle as these also have an effect on skin pigmentation and they turn otherwise black legs into clean yellow legs. If barred/cuckoo NN is your interest, you could mix them with whites for this reason.. they'd all be supposed to have as yellow legs as possible anyways...
Buff to red is not a good idea either, as buff is very complicated and hard to get even buff coloring.. getting buff roosters without darker shade saddles than body would be a big problem if they were crossed.
as you see- so much detail and differences, not an easy one to answer.
